US4706633A - Air/fuel ratio feedback control system adapted to temporary open-loop control under transient conditions - Google Patents

Air/fuel ratio feedback control system adapted to temporary open-loop control under transient conditions Download PDF

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Publication number
US4706633A
US4706633A US06/851,104 US85110486A US4706633A US 4706633 A US4706633 A US 4706633A US 85110486 A US85110486 A US 85110486A US 4706633 A US4706633 A US 4706633A
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engine
air
fuel ratio
warm
control
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US06/851,104
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English (en)
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Toyoaki Nakagawa
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Nissan Motor Co Ltd
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Nissan Motor Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1486—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor with correction for particular operating conditions
    • F02D41/1488—Inhibiting the regulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/04—Introducing corrections for particular operating conditions
    • F02D41/06—Introducing corrections for particular operating conditions for engine starting or warming up
    • F02D41/068—Introducing corrections for particular operating conditions for engine starting or warming up for warming-up

Definitions

  • This invention relates to a system for feedback control of the air/fuel ratio in an internal combustion engine, particularly an automotive engine, by using an oxygen sensor as an exhaust gas sensor to detect actual values of the air/fuel ratio.
  • the control system includes means to interrupt the feedback control and use open-loop control during transient acceleration or deceleration of the engine.
  • an oxygen sensor comprising a solid electrolyte cell is used to estimate actual values of the air/fuel ratio in the engine from the concentrations of oxygen in the exhaust gas, and a signal representative of the deviation of the actual air/fuel ratio from the target value is produced in an electronic control unit.
  • a feedback signal to control the functions of a fuel-feed or air-fuel proportioning device such as carburetor or fuel injector is produced.
  • a standard amount of fuel injection T p is varied according to the engine operating conditions and may be given by the equation (1):
  • K is a constant
  • Q a is the flow rate of air being taken into the engine
  • N is the revolving speed of the engine.
  • T i When feedback control of the air/fuel ratio is performed, a corrected amount of fuel injection T i is computed by using a feedback signal to cancel deviations of the actual air/fuel ratio from the target value.
  • T i is given by the equation (2):
  • C f is a weighting factor which is variable depending on some parameters of the engine operating conditions such as the temperature of the cooling water, degree of opening of the throttle valve, etc.
  • ⁇ is a feedback correction factor computed by the aforementioned proportional and/or integral treatment of an air/fuel ratio deviation signal
  • T s is a correction factor for compensation of a delay in the response of the fuel injector to a control or command signal.
  • the present invention proposes to vary the duration of the temporary open-loop control of the air/fuel ratio according to the degree of warm-up of the engine.
  • the invention provides a control system for feedback control of the air/fuel ratio of an air-fuel mixture supplied to an internal combustion engine, the control system comprising air/fuel ratio detection means for detecting actual values of air/fuel ratio in the engine from concentrations of oxygen in the exhaust gas of the engine, warm-up detection means for detecting the degree of warm-up of the engine, timing means for variably determining the duration of temporary open-loop control of the air/fuel ratio according to the detected degree of warm-up of the engine, transient condition detection means for detecting predetermined transient operating conditions of the engine, and control means for performing feedback control of the feed of fuel and/or air to the engine based on the detected actual values of air/fuel ratio.
  • air/fuel ratio detection means for detecting actual values of air/fuel ratio in the engine from concentrations of oxygen in the exhaust gas of the engine
  • warm-up detection means for detecting the degree of warm-up of the engine
  • timing means for variably determining the duration of temporary open-loop control of the air/fuel ratio according to the detected degree of warm-up
  • This control means comprises shift means for shifting the feedback control of the feed of fuel and/or air to open-loop control when any of the predetermined transient operating conditions of the engine is detected and for shifting the open-loop control to the feedback control after the lapse of a time the length of which has a predetermined relation to the duration of temporary open-loop control determined by the timing means.
  • the air/fuel ratio control system according to the invention is very suitable for application to automotive engines.
  • the duration of temporary open-loop control of the air/fuel ratio is made variable and is optimally adjusted according to the degree of warm-up of the engine.
  • the feedback control wherein temporarily interrupted upon detection of a transient operating condition of the engine, is resumed at an optimum time-point even when the feedback control is interrupted and shifted to open-loop control during a warm-up stage of the engine operation.
  • This is a good solution to a serious problem in commencing feedback control of the air/fuel ratio soon after starting the engine.
  • the duration of temporary open-loop control of the air/fuel ratio can be kept constant so as to be optimum in transient operating conditions of the warmed engine.
  • Most parts of the above named essential elements of the air/fuel ratio control system can be integrated in a microcomputer.
  • FIG. 1 is a block diagram showing the fundamental construction of an air/fuel ratio control system according to the invention
  • FIG. 2 is a diagrammatic illustration of an embodiment of the invention, which is an air/fuel ratio feedback control system for an automotive engine;
  • FIG. 3 is a schematic and sectional view of an oxygen sensor used in the system of FIG. 2;
  • FIG. 4 is an exploded view of the oxygen sensor of FIG. 3;
  • FIG. 5 is a simplified circuit diagram of an air/fuel ratio detection circuit included in the system of FIG. 2;
  • FIG. 6 is a graph showing the relationship between air/fuel ratio in the engine in FIG. 2 and a voltage signal produced in the circuit of FIG. 5;
  • FIG. 7 is a chart for explanation of fluctuations of actual air/fuel ratio in the engine in FIG. 2 resulting from feedback control of air/fuel ratio under a transient operating condition of the engine;
  • FIG. 8 is a flowchart showing a computer program for variably determining the length of a period for which the control of air/fuel ratio by a control system according to the invention is shifted to open-loop control;
  • FIG. 9 is a chart showing the manner of determining the length of the aforementioned period in relation to the degree of warm-up of the engine.
  • FIG. 10 is a flowchart showing a computer program stored in a microcomputer in a control system according to the invention for performing the control of air/fuel ratio under transient operating conditions of the engine.
  • FIG. 1 shows the functional connections between the principal elements of an air/fuel ratio control system according to the invention.
  • the control system includes an air/fuel ratio detection means 10 to detect the actual air/fuel ratio in an internal combustion engine by sensing the concentration of oxygen in the exhaust gas.
  • An electronic control unit 11 utilizes the air/fuel ratio signal produced by the detection means 10 to find any deviation of the actual air/fuel ratio from a target value and produces a fuel feed control signal, or an air intake control signal, which is supplied to an electromechanical means 12 for minutely regulating the ratio of air to fuel being taken into the engine.
  • the air/fuel ratio control system includes a temperature sensing means 13 to detect the degree of warm-up of the engine and another sensing means 15 to detect transient operating conditions of the engine.
  • the information obtained by the sensing means 15 is supplied to the control unit 11, which has the function of interrupting the feedback control of air/fuel ratio and leave the air/fuel ratio under open-loop control for a predetermined length of time when the supplied information indicates any of a set of predetermined transient operating conditions of the engine.
  • the information obtained by the warm-up detection means 13 is used in an adjusting means 14 to optimally determine the aforementioned length of time, i.e. feedback control interruption time, according to the degree of warm-up of the engine.
  • the adjusting means 14 informs the control unit 11 of the optimum length of time.
  • FIG. 2 shows an automotive internal combustion engine 20 provided with an air/fuel ratio control system which accomplishes its purpose by controlling the amount of fuel injection into the engine.
  • an intake passage 22 extends from an air cleaner 24 to the combustion chambers of the engine 20, and electromagnetically operated fuel injectors 26 open into the intake passage 22.
  • a catalytic converter 30 occupies an intermediate section for purifying the exhaust gas by means of a suitable catalyst such as a three-way catalyst.
  • an airflow meter 32 which produces a signal representative of the flow rate Q a of air being taken into the engine, and a sensor 36 is coupled with throttle valve $4 to produce a signal representative of the degree of opening C v of the throttle valve 34.
  • a crank-angle sensor 58 is provided to produce a signal representative of the engine revolving speed N.
  • a temperature sensor 40 is disposed in the cooling water jacket to produce a signal representative of the cooling water temperature T w . In this embodiment the cooling water temperture sensor 40 is employed as means to detect the degree of warm-up of the engine 20.
  • An oxygen sensor 50 is disposed in the exhaust passage 28 at a section upstream of the catalytic converter 30 to estimate an actual air/fuel ratio in the combustion chamber from the concentration of oxygen in the exhaust gas.
  • the type of the oxygen sensor 50 is not specified, so that a wide selection can be made from conventional and recently developed oxygen sensors.
  • the oxygen sensor 50 is comprised of an oxygen concentration cell using an oxygen ion conductive solid electrolyte and an oxygen ion pump cell which too uses a similar solid electrolyte.
  • An air/fuel ratio detection circuit 80 which is a part of the air/fuel ratio detection means 10 in FIG.
  • this circuit 80 1, measures the output voltage V s of the concentration cell in the oxygen sensor 50 and supplies a controlled pumping current I p to the pump cell in the sensor 50 so as to keep the output voltage V s at a predetermined level. Furthermore, this circuit 80 produces a voltage signal V i which is representative of the magnitude of the controlled pumping current I p and, therefore, is indicative of the actual air/fuel ratio.
  • the air/fuel ratio control system of FIG. 2 has a control unit -00 in which the control unit 11, the duration adjusting means 14, a part of the warm-up detection means 13 and a part of the transient condition detection means 15 shown in FIG. 1 are integrated.
  • This control unit 100 is a microcomputer comprised of CPU 102, ROM 100, RAM 106 and I/O port 108.
  • the ROM 104 stores programs of operations of CPU 102.
  • the RAM 106 stores various data to be used in operations of CPU 102, some of which are in the form of map or table.
  • the signals produced by the above described sensors 32, 36, 38 and 40 are input tO the I/O port 108 along with the air/fuel ratio signal V i produced in the detection circuit 80. Based on the engine operating condition information gained from these input signals the control unit 100 provides a fuel injection control signal S i to the injectors 26 so as to realize an intended air/fuel ratio.
  • the construction of the oxygen sensor 50 is, for example, as shown in FIGS. 3 and 4.
  • This oxygen sensor 50 is a laminate-like assembly of thin layers including a substrate 52 of a ceramic material such as alumina.
  • a heater element 54 is attached to or embedded in the substrate 52.
  • the bottom face of the solid electrolyte plate 60 is locally laid with an anode layer 62 which is to be exposed to the air admitted into the chamber 58.
  • a cathode layer 64 is formed on the top face of the solid electrolyte plate 60.
  • a spacer sheet 68 is bonded to the solid electrolyte plate 60 so as to cover the area (roughly half) not containing the cathode layer 64.
  • the thickness L of the spacer 68 is about 0.1 mm.
  • a second layer or plate 70 of an oxygen ion conductive solid electrolyte is bonded to the spacer 68 so as to lie opposite and parallel to the first solid electrolyte plate 60.
  • a gap 72 of the given width L exists between the first and second solid electrolyte plates 60 and 70.
  • the bottom face of the solid electrolyte plate 70 is covered with a cathode layer 76, which faces and is exposed in the gap 72.
  • An anode layer 74 is formed on the top face of the solid electrolyte plate 70.
  • the sensor 50 is disposed in the exhaust passage 28 such that the exhaust gas indicated by arrows G in FIG. 3 enters the aforementioned gap 72 while only the air (or an alternative oxygen-containing reference gas) is admitted into the chamber 58.
  • the combination of the first solid electrolyte plate 60 and the anode and cathode layers 62 and 64 serves as an oxygen concentration cell which generates a variable electromotive force or voltage V s according to a difference in oxygen partial pressure between the air existing on the anode side and the gas G existing on the cathode side. In the following description this combination will be called the sensor cell 66.
  • the combination of the second solid electrolyte plate 70 and the anode and cathode layers 74 and 76 will be called the pump cell 78.
  • an externally supplied DC current I p flows across the solid electrolyte plate 70 from the anode 74 toward the cathode 76, there occurs migration of oxygen ions through the solid electrolyte plate 70 from the cathode side toward the anode side. Therefore, the flow of the current I p in such a direction results in extraction of some oxygen from the gas G existin9 in the gap 72.
  • the pump cell 78 functions as an oxygen ion pump.
  • the transfer of oxygen from or into the gap 72 by the action of the pump cell 78 is effective for varying the partial pressure of oxygen within the gap 72. For this reason the magnitude of the output voltage V s of the sensor cell 66 can be varied by controlling the pumping current I p .
  • the heater 54 is incorporated in the sensor 50 to heat both the first and second solid electrolyte plates 60 and 70 when the exhaust gas temperature is not sufficiently high since the solid electrolyte material used in the sensor 50 is usefully active only at fairly elevated temperatures.
  • FIG. 5 shows the construction of the air/fuel ratio detection circuit 80 in the system of FIG. 2.
  • the circuit 80 includes a DC power source 82 which provides a target volta V a .
  • a differential amplifier 84 is used to compare the output voltage V s of the sensor cell 66 of the oxygen sensor 50 with the target voltage V a and to produce a voltage signal ⁇ V which represents the difference V s -V a .
  • This circuit 86 receives the output ⁇ V of the differential amplifier 84 and varies the polarity and magnitude of the current I p so as to nullify the differential voltage ⁇ V by the function of the pump cell 78.
  • the current supplying circuit 86 functions so as to increase the pumping current I p when the differential voltage ⁇ V is positive and to decrease the current I p when ⁇ V is negative.
  • the pumping current I p is positve when flowing in the direction of the arrow in broken line and negative when flowing in the direction of the arrow in solid line.
  • the path of the current I p includes a resistance 88 which is used to detect the magnitude of the pumping current I p . That is.
  • a current detection circuit 90 produces a voltage signal V i which is proportional to a voltage drop across the resistance 88. Naturally. V i is proportional to I p .
  • the target voltage V a is set at such a value that the output voltage V s of the oxygen sensor 50 becomes equal to V a when the concentration of oxygen in the gas within the gap 72 in the oxygen sensor 50 is as expected under the desired air/fuel ratio condition or, in other words, when the oxygen partial pressure ratio between the anode 62 and the cathode 64 of the sensor cell 66 is as expected.
  • the current I p or indication voltage V i produced by the current detection circuit 90 varies with the actual air/fuel ratio of the mixture supplied to the engine.
  • the air/fuel ratio and the indication voltage V i As shown in FIG. 6, wherein the air/fuel ratio on the abscissa is represented by excess air factor ( ⁇ ). Therefore, by utilizing the indication voltage V i it is possible to accurately and continuously detect the actual air/fuel ratio over a wide range including both fuel-rich conditions and lean conditions.
  • the control unit 100 utilizes the output V i of the air/fuel ratio detection circuit 80 as an air/fuel ratio signal and produces the fuel injection control signal S i , which corresponds to the corrected amount of fuel injection T i given by the equation (2), by first finding a difference between the input signal V i and a reference signal representing the target value of the air/fuel ratio and then making proportional and/or integral treatment of the value of the difference. Accordingly deviations of the actual air/fuel ratio from the target value under normal operating conditions of the engine can soon be corrected.
  • control unit 100 continues to estimate the operating conditions of the engine 20 by using information supplied from, for example, the aforementioned sensors 32, 36, 38, 40 to optimally adjust the weighting factor C f in computing the corrected amount of fuel injection T i by the equation (2). Furthermore, the control unit 100 has the function of shifting the feedback control of air/fuel ratio to open-loop control when the engine is judged to be operating under predetermined transient acceleration or deceleration conditions. The main reason for such interruption of the feedback control is that the actual air/fuel ratio detected by using the oxygen sensor 50 does not accurately follow a sudden and great change in the amount of fuel injection T i . For instance, FIG.
  • the actual air/fuel exhibits a gradual rise.
  • the decrease of T i is terminated at a suitably fixed level the gradually rise in the actual air/fuel ratio still continues for a while, and at time-point t 2 the actual air/fuel ratio stabilizes at a level corresponding to the fixed level of T i .
  • the actual air/fuel ratio differs significantly from the calculational air/fuel ratio established by the function of the control unit 100 during the period T t between t 1 and t 2 , it is inappropriate to continue feedback control of air/fuel ratio during this period T t .
  • the length of this period T t cannot exactly be measured and is variable depending on several factors and particularly on the degree of warm-up of the engine. In general T t becomes longer as the engine temperature is lower.
  • the duration of the temporary open-loop control TD is varied according to the degree of warm-up of the engine so that always TD may not greatly differ from a period represented by T t in FIG. 7 for which the feedback control is really inappropriate.
  • the operations of the control unit 100 will be described with reference to FIGS. 8 and 9.
  • the flowchart of FIG. 8 is one of the computer programs stored in the ROM 104. This program is repeatedly executed at a predetermined time interval.
  • T w is read in.
  • T h is in the range of from 50° to 90° C. It T w is not higher than T h , the operation proceeds to the step P3 based on a judgment that the warm-up is still incomplete.
  • an optimum value of the duration TD of temporary open-loop control is found by table look-up.
  • the relationship between T w and TD which is generally as shown in FIG. 9, is stored as a table in the RAM 106.
  • step P4 TD is set at a predetermined high-temperature value TD h . That is, TD is minutely varied until completion of the engine warm-up and is kept at a fixed value TD h after completion of the warm-up.
  • FIG. 10 shows another computer program stored in the ROM 104 for temporarily shifting the feedback control of air/fuel ratio to open-loop control under predetermined transient operating conditions of the engine. This program too is repeatedly executed at a predetermined time interval.
  • the feedback control of the air/fuel ratio using the oxygen sensor 50 is temporarily shifted to open-loop control whenever a predetermined transient operating condition of the engine is detected.
  • the duration TD of the temporary open-loop control is set in advance. That is, while the feedback control is performed the duration TD is always adjusted to an optimum value according to the degree of warm-up of the engine. In a strict sense, the actual duration of the open-loop control is longer than the preset duration TD by a short period of time required for ascertainment of a transient operating condition of the engine. In practice, however, it suffices to consider the duration TD which is measured from the moment of commanding to shift the feedback control to open-loop control.
  • the duration TD of temporary open-loop control may be assigned with two different values one of which is to be used when the detected transient operating condition is an accelerating condition and the other for use in the case of a decelerating condition.
  • the single value of TD at each degree of warm-up of the engine may be corrected according to the rate of acceleration or deceleration. Either of these measures is effective for further enhancement of precision of the control of air/fuel ratio.
  • the degree of warm-up of the engine can be detected also by measuring the temperatures in the intake or exhaust manifold, intake ports and/or the cylinder head or the temperature of intake air instead of the cooling water temperature.
  • the type and construction of the oxygen sensor 50 illustrated in FIGS. 3 and 4 are merely by way of example and are not the least limitative.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
US06/851,104 1985-04-22 1986-04-14 Air/fuel ratio feedback control system adapted to temporary open-loop control under transient conditions Expired - Lifetime US4706633A (en)

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JP60086159A JPS61244848A (ja) 1985-04-22 1985-04-22 空燃比制御装置
JP60-86159 1985-04-22

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4782690A (en) * 1985-07-17 1988-11-08 Nissan Motor Co., Ltd. Air/fuel ratio detecting apparatus, and method of detecting normal and abnormal conditions of the sensor
US4958611A (en) * 1988-03-01 1990-09-25 Mitsubishi Denki Kabushiki Kaisha Air-fuel ratio controller of internal combustion engine
US5564404A (en) * 1994-09-20 1996-10-15 Nissan Motor Co., Ltd. Air/fuel ratio control system of internal combustion engine
US5758308A (en) * 1994-12-30 1998-05-26 Honda Giken Kogyo Kabushiki Kaisha Fuel metering control system for internal combustion engine

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6483836A (en) * 1987-09-24 1989-03-29 Fuji Heavy Ind Ltd Air-fuel radio controller for engine
JP3063186B2 (ja) * 1991-03-07 2000-07-12 株式会社デンソー エンジンのアイドリング回転数制御装置
DE19917440B4 (de) * 1999-04-17 2005-03-24 Robert Bosch Gmbh Verfahren zur Steuerung des Luft-Kraftstoff-Gemisches bei extremen Dynamikvorgängen
DE10004416A1 (de) * 2000-02-02 2001-08-09 Delphi Tech Inc Verfahren zum Einstellen des Luft-Kraftstoff-Verhältnisses bei einem Verbrennungsmotor
DE10255364B4 (de) * 2001-11-29 2006-03-30 Hitachi, Ltd. Vorrichtung und Verfahren zur Steuerung des Luft/Kraftstoff Verhältnisses in einem Verbrennungsmotor
JP6762219B2 (ja) * 2016-12-15 2020-09-30 株式会社ケーヒン 内燃機関制御装置

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US4388905A (en) * 1980-07-16 1983-06-21 Fuji Jukogyo Kabushiki Kaisha Air-fuel ratio control system
US4419975A (en) * 1980-10-11 1983-12-13 Fuji Jukogyo Kabushiki Kaisha Air-fuel ratio control system
US4545348A (en) * 1979-05-22 1985-10-08 Nissan Motor Company, Ltd. Idle speed control method and system for an internal combustion engine
US4580539A (en) * 1984-02-27 1986-04-08 Nissan Motor Co., Ltd. Air-fuel ratio control apparatus

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JPS5828566A (ja) * 1981-07-24 1983-02-19 Toyota Motor Corp 内燃機関の空燃比制御方法および装置
JPS5827847A (ja) * 1981-08-13 1983-02-18 Toyota Motor Corp 内燃機関の空燃比制御方法及びその装置
JPS58124044A (ja) * 1982-01-21 1983-07-23 Nippon Denso Co Ltd 内燃機関の空燃比制御装置
JPS58214626A (ja) * 1982-06-08 1983-12-13 Toyota Motor Corp 燃料噴射内燃機関の空燃比制御装置
JPS60230532A (ja) * 1984-04-28 1985-11-16 Toyota Motor Corp 内燃機関の空燃比制御装置

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Publication number Priority date Publication date Assignee Title
US4545348A (en) * 1979-05-22 1985-10-08 Nissan Motor Company, Ltd. Idle speed control method and system for an internal combustion engine
US4388905A (en) * 1980-07-16 1983-06-21 Fuji Jukogyo Kabushiki Kaisha Air-fuel ratio control system
US4419975A (en) * 1980-10-11 1983-12-13 Fuji Jukogyo Kabushiki Kaisha Air-fuel ratio control system
US4580539A (en) * 1984-02-27 1986-04-08 Nissan Motor Co., Ltd. Air-fuel ratio control apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4782690A (en) * 1985-07-17 1988-11-08 Nissan Motor Co., Ltd. Air/fuel ratio detecting apparatus, and method of detecting normal and abnormal conditions of the sensor
US4958611A (en) * 1988-03-01 1990-09-25 Mitsubishi Denki Kabushiki Kaisha Air-fuel ratio controller of internal combustion engine
US5564404A (en) * 1994-09-20 1996-10-15 Nissan Motor Co., Ltd. Air/fuel ratio control system of internal combustion engine
US5758308A (en) * 1994-12-30 1998-05-26 Honda Giken Kogyo Kabushiki Kaisha Fuel metering control system for internal combustion engine

Also Published As

Publication number Publication date
JPS61244848A (ja) 1986-10-31
JPH0461180B2 (ja) 1992-09-30
DE3613570A1 (de) 1986-10-23
DE3613570C2 (ja) 1988-09-01

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